Method of manufacturing an electrical lead

ABSTRACT

An electrically conductive member ( 10 ) includes an elongate body ( 11 ) which has at least one electrically conductive region ( 20 ). The electrically conductive region ( 20 ) comprises a porous polymeric material coated with an electrically conductive material. A method of manufacturing the electrically conductive member ( 10 ) includes the steps of extruding an elongate body of polymeric material wherein at least one region of the elongate body is porous in nature; and coating said elongate body with an electrically conductive material such that the electrically conductive material substantially coats the pores of said at least one region.

FIELD OF THE INVENTION

The present invention relates to medical electrical leads and electrodes and in particular to medical leads having electrodes made from a metal-coated polymeric material.

BACKGROUND ART

Electrical leads and electrodes are commonly utilised in the medical field for applications such as stimulation, sensing, ablation and defibrillation.

Traditionally, medical electrodes comprise machined metal or coiled metal wire components which, while suitably conductive, do not provide the flexibility in both design and mechanical properties afforded by a metal coated polymer. Furthermore, metal coated polymers are particularly suitable for use in larger area electrodes where their light weight, flexibility and versatility are key advantages.

The use of metal coated or metal filled polymers as medical electrodes has been considered. For example, in U.S. Pat. No. 5,279,781, a metal filled fibre for use as a defibrillation electrode is described. The metal in this case is added during the spinning process. To render the electrode suitably conductive, however, requires the addition of a significant proportion of metal to the fibre which in turn has an adverse effect on the mechanical strength of the electrode.

Further structures, including metal filled silicones and intrinsically conductive polymers, have been considered for use as medical electrodes although it has been found that such structures do not have the required level of conductivity necessary for the abovementioned medical applications.

Typically, the problem encountered with using a polymeric material as an electrode is that it is difficult to obtain a good electrical connection to the electrode. In U.S. Pat. No. 5,609,622, an electrical connection was achieved by utilising an electrode having metal wires embedded in its wall. The electrode was then subjected to an ion beam treatment with metal such that the metal was deposited within the wall and therefore contacted the wires. In this case, however, the electrical connection was only shown to occur at one end of the electrode and further, it is questionable whether a good connection is achieved by this method as it relies upon the incidence of metal contacting wire through the thickness of the plastic.

The present invention provides an electrical lead and/or electrode which overcomes the problems of the prior art.

Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.

DISCLOSURE OF THE INVENTION

Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

According to a first aspect, the present invention is an electrically conductive member including an elongate body, the body having at least one electrically conductive region, the region comprising a porous polymeric material coated with an electrically conductive material.

Preferably, the electrically conductive member is adapted for medical use and in particular, but not limited to, use in cardiac mapping, defibrillation or pacing, neurological applications including neural stimulation implants, muscle stimulation, sensing and ablation. Accordingly, in a preferred embodiment, the electrically conductive member may comprise part of a lead or any other form of carrier.

Typically, the electrically conductive member is an elongate tube. While the entire length of the member may be made from a porous polymer coated with an electrically conductive material it is also envisaged that the electrically conductive member may comprise a plurality of distinct electrically conductive regions made up of the coated porous polymer.

In the embodiment wherein the electrically conductive member is tubular, it is preferred that the pores of the at least one electrically conductive region are present substantially across the diameter of a side wall of the tubular structure. Accordingly, in this embodiment, electrical connection may be made from internal a lumen of the tube. It is further envisaged that electrical connection may be made from within the side wall of the tube as further discussed below.

Rather than a tube, the electrically conductive member may comprise a solid cylindrical member. In this embodiment, it is again preferred that the pores of the at least one electrically conductive region are present substantially across the diameter of the cylindrical member.

In a preferred embodiment, the pores of the polymeric material of the at least one electrically conductive region are greater than 5 microns and preferably between 30 and 100 microns. When the porous polymeric material is coated with an electrically conductive material, said electrically conductive material preferably coats and lines at least some of, and preferably all of, the pores.

Typically, the electrically conductive material is a metal and, preferably, a biocompatible metal such as platinum. It is envisaged that a combination of two or more metals or metal alloys may be used, however, to improve electrical conductivity. For example, it may be desirable to provide a first layer of copper or silver or any other suitably conductive metal and a second layer of platinum to enable use of the electrically conductive member within a body.

The coating of the porous polymeric material preferably creates a suitably thick layer of metal coating across the at least one electrically conductive region. Preferably, the resistance of the coating is less than 100 ohms and more preferably less than 10 ohms.

The porous polymeric material may be expanded polytetrafluoroethylene (PTFE) wherein the pore size is adjusted to allow the metal coating to penetrate the pores and to produce a coating of sufficient thickness to provide adequate electrical conductivity. Other materials are envisaged including, but not limited to, porous silicones, porous polyurethanes, polyether block amide (PEBAX) or nylon. In each case, the pore size may be varied depending upon the method of formation of the porous material or by the addition of additives such as sodium chloride (NaCl), sodium bicarbonate (Na₂HCO₃) or polyglycolide which can be leached out following moulding or extrusion leaving a porous structure.

Alternatively, the pores of the polymeric material may be formed by drilling into the polymer using a laser drill. This has the particular advantage of enabling only a portion of the polymer to be of a porous nature.

The at least one electrically conductive region may be electrically connected to an electrical conductor.

In one embodiment, the electrical conductor is a straight or coiled wire, or number of wires, embedded within the body of the electrically conductive member and preferably within the at least one electrically conductive region of the member. If the electrically conductive member is a solid cylindrical member, the wire or wires may be coiled in a helical manner within the at least one electrically conductive region. If the electrically conductive member is a tubular structure, the wire or wires may be coiled in a helical manner within the wall of the tube and preferably within the at least one electrically conductive region. In either embodiment, the wire(s) may extend through several pores of the at least one electrically conductive region. Accordingly, when the porous polymeric material of the at least one region is coated with the electrically conductive material, the portions of wire which extend through the pores may be simultaneously coated with the electrically conductive material thereby creating a good electrical connection between the electrical conductor and the electrically conductive region.

The wires may be single wires or multifilament wires. Further, the wire or wires may be made of copper preferably coated with a noble metal such as palladium or platinum for corrosion resistance. Alternatively, the individual wires may be a multifilament stainless steel wire. Other suitable materials include, but are not limited to, platinum or platinum alloy, MP₃₅N or Elgiloy.

In the above embodiment, depending upon the application of the electrically conductive member, the wire(s) may be connected by an insulated conductor to either a source of electricity or to an analyser means. Typically, the wire(s) are connected to the insulated conductor by way of welding. Alternatively, they may be connected by electrically conductive adhesives or by soldering.

In a further embodiment, the electrical conductor is located internal the elongate body of the electrically conductive member. For example, if the electrically conductive member is a tube having at least one electrically conductive region, the electrical conductor may be positioned within the lumen of the tube. In this embodiment, the electrical conductor is preferably adapted such that it engages the internal surface of the tube. To ensure that the electrical conductor engages the tube, it is preferred that the electrical conductor comprises a resilient spring, such as a spiral spring that, once positioned in the tube, can expand into contact with the inner wall of the tube.

In another embodiment, the electrical conductor may be a spring formed from a shape memory alloy such as Nitinol™. The shape memory spring preferably moves, when exposed to a pre-determined temperature, from a first position to a second position wherein when in the second position, the spring expands such that it has an outer diameter greater than the inner diameter of the tube. Accordingly, when internal the lumen of the tube and when in the expanded second position, the spring engages the inner surface of the tube to a sufficient extent to provide a good electrical connection between the electrical conductor and the at least one electrically conductive region.

In one embodiment, the shape memory alloy spring expands into contact with the inner surface of the tube upon exposure to body temperature.

The shape memory spring may be connected to an insulated conductor by welding, the use of electrically conductive adhesives or soldering.

In the above embodiments, it is preferred that the electrical conductor such as the wire(s) embedded within the electrically conductive member or a shape memory alloy spring positioned within a lumen of a tubular electrically conductive member, extends the entire length of the electrically conductive member, or at least the length of the at least one electrically conductive region, such that a good electrical connection between the electrical conductor and the at least one electrically conductive region can be made.

In another embodiment, the electrical conductor is adapted to engage an end of the electrically conductive member. For example, the electrical conductor may include a shape memory alloy tube that is adapted to expand and increase its internal diameter upon heating above a pre-determined temperature or exposure to a particular pre-determined temperature. The shape memory alloy tube may then be slid over an end of the electrically conductive member. Upon heating above or cooling below the pre-determined temperature depending on the type of shape memory alloy, the shape memory alloy tube preferably returns to its original unexpanded shape therefore effectively clamping down on an end of the electrically conductive member. This embodiment provides a uniform radial pressure on the end of the member and provides a good electrical connection between the electrical conductor and the at least one electrically conductive region of the member. If the electrically conductive member is a tube, it may be necessary to provide an inner tube which is relatively stiff and which may be positioned internal the lumen of the tube to prevent collapse of the member.

In a second aspect, the present invention consists in a method of manufacturing the electrically conductive member of the first aspect, said method comprising the steps of:

(i) extruding an elongate body of polymeric material wherein at least one region of the elongate body is porous in nature; and

(ii) coating said elongate body with an electrically conductive material such that the electrically conductive material substantially coats the pores of said at least one region.

While the entire length of the elongate body may be coated with the electrically conductive material, in the embodiment wherein there are distinct regions of porous polymeric material, it may be preferred that only the distinct porous regions are coated with said electrically conductive material rather than the entire length of the elongate body which may include non-porous regions.

Where the electrical conductor comprises a straight or coiled wire, the electrically conductive member may be manufactured in a number of stages. For example, a first tube, or layer, or solid cylindrical member may be formed from either a porous polymeric material or non-porous polymeric material or a combination thereof. The wire may then be wrapped around and along at least a portion of the first tube or solid cylindrical member in a helical manner or extended along at least a portion of the length of the first tube or layer or solid cylindrical member. The wire and the first tube or layer or solid cylindrical member may then be overlaid with a coating or another layer. The coating or the other layer may be a porous polymeric material or alternatively, a polymeric material having regions which are of a porous nature. In one embodiment, the coating may be a second tube.

In a further embodiment of the second aspect, the electrically conductive member may comprise a tube. In this embodiment, the electrical conductor is positioned within the lumen of the tube. The electrical conductor is preferably positioned such that it engages the internal surface of the tube. To ensure that the electrical conductor engages the tube, it is preferred that the electrical conductor comprises a resilient spring, such as a spiral spring that, once positioned in the tube, can expand into contact with the inner wall of the tube.

In another embodiment of the second aspect, the electrical conductor can be formed in a spring form from a shape memory alloy such as Nitinol™. The shape memory spring can preferably move from a first position to a second position wherein when in the second position, the spring could expand such that it had an outer diameter greater than the inner diameter of the tube.

The electrical conductor may be adapted to engage an end of the electrically conductive member. For example, the electrical conductor may include a shape memory alloy tube that is adapted to expand and increase its internal diameter upon heating above a pre-determined temperature. The shape memory alloy tube may then be slid over an end of the electrically conductive member. Upon heating above or cooling below the pre-determined temperature depending on the type of shape memory alloy, the shape memory alloy tube preferably returns to its original unexpanded shape therefore effectively clamping down on an end of the electrically conductive member. This embodiment provides a uniform radial pressure on the end of the electrically conductive member and provides a good electrical connection between the electrical conductor and the at least one electrically conductive region of the member.

Typically, the electrically conductive material is applied to the elongate body or preferably to the at least one electrically conductive region using a wet technique such as electroless plating. In this embodiment, the electrically conductive material may be forced through the pores of the at least one electrically conductive region by the application of pressure.

Alternatively, the electrically conductive material may be applied by electroless plating followed by the additional step of electroplating.

Each of the above processes preferably ensures that a coating of electrically conductive material penetrates substantially all the pores of the electrode. If the at least one region of electrically conductive material has pores disposed substantially throughout the entire thickness of said region, it is envisaged that electrical connection may be made by way of an electrical conductor, as described above, either within the wall of the elongate body or on the inside of the elongate body (for example if the elongate body is a tubular structure).

The process of coating the elongate body with an electrically conductive material such that the pores of the at least one electrically conductive region are coated with such a material may involve a number of steps prior to the actual coating with the electrically conductive material. The steps include:

(1) Cleaning.

(2) Surface Modification.

(3) Catalysis.

(4) Coating.

(1) The material to be coated is typically washed in an organic solvent such as acetone or ethyl acetate or in a solution containing a suitable surface active agent. Usually some agitation is required such as from an ultrasonic cleaner or a shaker water bath. The step of cleaning may be carried out above room temperature.

(2) The step of surface modification results in a more wettable or hydrophilic surface such that the deposition of the coating may be accelerated and, further, chemical and mechanical adhesion of the coating to the surface may be improved.

Chemical adhesion may be improved by creating the most suitable functional groups on the surface of the polymer such as amides, while mechanical adhesion may be improved by creating a roughened surface using chemical (etching) or mechanical (sandblasting) methods.

Typically, the surface modification chemicals are infused into the pores using pressure via a pump or syringe. Alternatively, the porous material to be coated may be placed in the treatment solution and evacuated in a vacuum thereby removing gas bubbles from within the porous structure resulting in contact of all surfaces with the treatment solution.

Additionally, plasma treatment may be used to improve wettability and/or improve chemical or mechanical adhesion.

Following this step, the structure to be coated is rinsed several times preferably in deionised water.

(3) The catalyst step results in the deposition of a small amount of noble metal on the surface of the material. This provides the sites for deposition of the coating material, for example, platinum. While typical electroless plating uses a tin/palladium catalyst it is preferred that a process which eliminates the tin is used. For example, palladium in an acidic aqueous solution or dimethyl sulfoxide both of which can be reduced in a hydrazine solution is preferred. The latter is particularly useful as, being an organic solution, it allows improved wettability for many substrates.

In one embodiment of the catalysis of a material such as silicone, the catalyst, in the form of palladium metal powder can be mixed into a silicone dispersed in a solvent and then infused into the pores and cured prior to coating. In this embodiment, a small concentration of actual silicone is required so as to provide a thin layer on the surface of the pores rather than fill the pores with silicone. The palladium metal will act as a catalyst and will be bound to the silicone and therefore increase the adhesion of the coating material which is subsequently applied.

Alternatively, the silicone mix may be infused with palladium prior to moulding or extrusion.

The catalyst step may be performed a number of times.

(4) The coating process preferably uses electroless plating wherein a number of metals may be deposited using either commercially available or custom made solutions of complex metal ions together with a stabiliser and an added reducer. The solution typically allows controlled deposition of a metal over a specific period of time. If a biocompatible electrode is required, it is preferred that the metal is platinum.

A fifth step may be added to the above process if a thicker coating of metal and therefore higher conductivity is required. This would involve further electroless plating or electroplating.

In a further embodiment, following the process of coating, the pores are infused with a liquid adhesive such as, but not limited to, a silicone dispersant to effectively seal the pores. Preferably the infusion of the adhesive is carried out from within the electrically conductive member when said member is a tubular structure. This embodiment has the advantage of enabling an electrically conductive member to be implanted in a body for long periods of time with minimal tissue ingrowth into the member. This facilitates easy removal of the member if required.

In a third aspect, the present invention consists in an electrically conductive member including an elongate body, said elongate body having at least one electrically conductive region comprising a polymeric material together with at least one electrical conductor wherein at least a portion of the polymeric material and at least a portion of the at least one electrical conductor have a coating thereon of an electrically conductive material.

Preferably, the elongate body comprises a tubular body made of a suitable polymer material. The electrical conductor is preferably housed within at least part of a side wall of the tubular body. In addition to being housed within a side wall of the tubular body at the at least one electrically conductive region of the body, the electrical conductor may extend along the entire length of the tubular body.

The elongate body preferably comprises a first cylindrical inner member and a second outer member, said second outer member substantially forming a coating around the first inner member. The second outer member preferably extends over the entire length of the first inner member. The at least one electrical conductor is preferably sandwiched between the first inner member and the second outer member.

The first inner member may be made from a suitable polymeric material such as polyurethane, polyether block amide (PEBAX), PEEK or polyimide. The second outer member is preferably formed from a similar polymeric material to that of the first inner member. Further, it is preferred that the second outer member is made from a transparent or at least substantially transparent material such that the at least one electrical conductor may be viewed through the second outer member.

Preferably, the second outer member is much thinner than the first inner member and typically, the second outer member is sufficiently thick to only just cover the at least one electrical conductor.

The at least one electrical conductor may comprise a metal wire or wires made from material such as PFA, polyimide insulated copper wire(s) or copper alloy wire(s). Preferably, the wire(s) have a diameter of approximately 0.025 to 0.3 mm.

Typically, during manufacture, single wires may be wound substantially around the circumference of the first inner member. Preferably, between 8 to 24 wires are wound around the first inner member in this manner wherein each wire has a predetermined spacing between it and the next wire. Said 8 to 24 wires may form a particular group which is spaced from a second or subsequent group of wires by a gap which is preferably larger than the gap between each wire of each group. In this way, identification of each group may be more easily determined. To aid identification, each group may further be colour coded.

The at least one electrical conductor may be helically wound around the first inner member. However, the present invention is not limited to the particular arrangement of the at least one electrical conductor and a number of combinations and orientations are envisaged.

Preferably at least one portion of the at least one electrical conductor, is not overlaid by the second outer member, that is, the at least one portion is exposed to the outside environment. The at least one portion of the electrical conductor this embodiment is preferably coated with the electrically conductive material. It is further preferred that at least a portion of the polymeric elongate body adjacent the exposed portion of the electrical conductor is also coated with the electrically conductive material.

Typically, a band around the circumference of the elongate body is coated together with the exposed portion of the electrical conductor to form a band electrode on the elongate body.

Preferably, the electrically conductive material is a metal and, preferably, a biocompatible metal such as platinum. It is envisaged that a combination of two or more metals or metal alloys may be used, however, to improve electrical conductivity. For example, it may be desirable to provide a first layer of copper or silver or any other suitably conductive metal and a second layer of platinum to enable use of the electrically conductive member within a body.

It is preferred that the exposed at least one portion of the electrical conductor is protected from corrosion. This may be achieved by, for example, immersing the elongate body in a solution such as palladium chloride which will coat the exposed portion(s).

In a fourth aspect, the present invention provides a method of manufacturing an electrically conductive member, the method comprising the steps of:

(i) extruding an elongate inner member from a polymeric material;

(ii) applying at least one electrical conductor to an exposed surface of the inner member;

(iii) overlaying the inner member and the at least one electrical conductor with an outer member made from a polymeric material such that the at least one electrical conductor is covered by said outer member;

(iv) exposing at least a portion of the at least one electrical conductor; and

(v) coating said exposed portion of the at least one electrical conductor and at least a portion of the outer member with an electrically conductive material.

Preferably, the inner member is extruded as a tube made from a suitable material such as polyurethane or polyether block amide (PEBAX).

The at least one portion of the at least one conductor may be exposed by a number of means including, but not limited to, applying heat, chemicals or lasers to remove the area of the outer layer covering the at least one portion. Desirably, a laser technique is used (eg quadruple Yag laser) as such a technique provides good accuracy. For example, the laser beam is capable of following a particular path of, say, a helically wound wire acting as the at least one electrical conductor. While, only a small portion of the at least one conductor may be exposed in this manner, the present invention is not limited to the amount of conductor exposed and, indeed, the entire conductor may be exposed.

For high energy applications, such as radio frequency (RF) or microwave ablation, adjacent electrical conductors may be exposed and coated with electrically conductive material to form a single electrode. Such a configuration decreases the current density. The electrical conductors of this embodiment may be electrically connected to each other at a proximal end of each electrical conductor. The number of electrodes formed together with the spacing between each electrode may be varied.

The exposed portion of electrical conductor(s) may be protected from corrosion by immersion in an acidic solution of, for example, palladium chloride, which will coat all the exposed portions.

It is desirable that the at least one portion of the at least one electrical conductor and at least a portion of the elongate body which together are coated to form an electrode are catalysed. To prevent catalysis of the remainder of the elongate body or electrical conductor which form a non-electrode area, these areas are protected from catalysis by masking them by, for example, photolithography or by using pieces of heat shrink tubing such as PET to protect said areas. An alternative to masking is the use of an ink which is pad printed over the areas to be coated and thus the areas which are to become the electrodes. The ink used may, or may not be electrically conductive but in any event should be able to catalyse a subsequent plating step. If radio opacity is required it may be desirable to use an ink including colloidal palladium or silver.

The catalyst step results in the deposition of a small amount of noble metal on the surface of the material to be coated. This provides the sites for deposition of the electrically conductive material, for example, platinum. While typical electroless plating uses a tin/palladium catalyst it is preferred that a process which eliminates the tin is used. For example, palladium in an acidic aqueous solution or dimethyl sulfoxide both of which can be reduced in a hydrazine solution is preferred. The latter is particularly useful as, being an organic solution, it allows improved wettability for many substrates.

The catalyst step may be performed a number of times.

The coating process preferably uses electroless plating wherein a number of metals may be deposited using either commercially available or custom made solutions of complex metal ions together with a stabiliser and an added reducer. The solution typically allows controlled deposition of a metal over a specific period of time. If a biocompatible electrode is required, it is preferred that the metal is platinum.

If relatively thick coatings are required, it is preferred that a porous polymer is used.

The electrodes formed with respect to the third and fourth embodiments, may be protected by a layer of, for example polyethylene glycol or mannitol. Such a protective layer preferably allows an electrical charge to pass therethrough.

The following examples describe the preparation of the electrode according to several embodiments of the first and second aspects of the present invention.

EXAMPLE 1

A porous polyurethane tube was made using a spraying system. Firstly a wire mandrel was connected to an electrical motor using a chuck. The wire was the simultaneously coated with a mixture of polyurethane (Pellethane) dissolved in dimethylformamide (1% polyurethane) and water. The water polymerised the polyurethane prior to deposition creating a porous layer. A copper wire was then wound onto the coated mandrel and a further layer was uniformly coated with the mixture of polyurethane dissolved in dimethylformamide and water. The spraying continued until the appropriate diameter was achieved ie. 2.2 mm (this was chosen as once assembled into a lead. a 2.2 mm lead body would comfortably pass down a 7 French introducer).

The porous component was then coated with platinum using the normal cleaning, surface modification, catalysis and coating steps previously outlined.

The resistance was then measured to be approximately 0.5Ω for a 1 cm length of the porous component, and approximately 1Ω from the end of the copper wire to the surface of the component.

EXAMPLE 2

An expanded PTFE tube was supplied by Impra which had a pore size of 30 microns. The tube was immersed in alcohol and placed in an ultrasonic cleaner to remove air bubbles and wet the surface.

The sample was removed from the alcohol and etched for 1 minute with FluoroEtch from Acton. A syringe was used to try and force the solution through the pores however this was unsuccessful.

The tube was then catalysed using a 2 g/l solution of PdCl₂ in Dimethyl Sulfoxide for 5 minutes intermittently attempting to force the solutions through the pores. This was followed by a reduction step in 4% Hydrazine solution.

The catalysed tube was then electrolessly coated using a platinum complex solution and hydrazine.

After 1.5 hours the sample was a shiny, metallic colour on the outside.

After drying, the resistance along the surface was found to be approximately 20Ω for a 1 cm length, however the resistance through the thickness varied from 25-50Ω.

EXAMPLE 3

Another expanded PTFE tube was supplied by Impra however this time the pore size was increased to 90 microns. The tube was immersed in alcohol and placed in an ultrasonic cleaner to remove air bubbles and wet the surface.

The sample was removed from the alcohol and etched for 30 seconds with FluoroEtch from Acton. A syringe was used to try and force the solution through the pores. This time the solution was able to freely pass through the structure.

The tube was then catalysed using a 2 g/l solution of PdCl₂ in Dimethyl Sulfoxide for 5 minutes intermittently forcing the solutions through the pores. This was followed by a reduction step in 4% Hydrazine solution.

The catalysed tube was then electrolessly coated using a platinum complex solution and hydrazine intermittently forcing the solution through the pores

After 1.5 hours the sample was a shiny, metallic colour on the outside.

After drying, the resistance along the surface was found to be approximately 1.5Ω for a 1 cm length. The resistance through the thickness was approximately 1.5Ω. No materials were removed using a standard tape test to measure adhesion.

A 4 mm length was then cut and a 2.1 mm diameter Nitinol™ spring (from Microvena, White Bear Lake Minn. USA) was straightened and passed up the middle of the cut platinum coated tube. The structure was then placed in the oven at 70° C. and the Nitinol™ spring went back to its original shape clamping on the inside of the platinum coated tube.

A length of 0.2 mm diameter copper wire was then welded to one end of the Nitinol spring. The resistance was found to be 1.8 ohms from the end of the copper wire and the outside of the platinum coated expanded Teflon.

A PEBAX tube was passed over each end of the spring and then glued with epoxy forming a butt joint on each side of the platinum coated expanded Teflon component.

After curing the lead was then tested in an isolated cow heart, by immersing the heart with electrode attached into a conductive media and RF energy passed through the electrode to the heart creating lesions. The test device produced similar lesions to a commercially available ablation lead.

The same lead was tested when delivering pacing pulses and a suitable impedance resulted.

Due to flexibility and versatility the electrodes can be made different shapes, sizes, numbers and spacing. This is important when designing new leads for various applications eg ablation leads for treating atrial fibrillation.

The following examples describe the preparation of the electrode according to several embodiments of the third and fourth aspects of the present invention.

EXAMPLE 4

A 1.6 mm diameter cable was sourced from MicroHelix in Portland Oreg. The cable contained 8 insulated wire coils in the wall of the tube. The insulating layer was made from a thin layer of PEBAX. Over one of the wires, a 4 mm length of insulation was removed to expose the corresponding amount of wire. A 4 mm band of the cable around the exposed wire was masked. Some plateable conductive ink from Creative Materials (CMI 117-31) Tyngsboro Mass. was coated around the unmasked region covering the exposed conductor. The electrode with ink was then immersed in a platinum complex electroless bath and coated for 1 hour at 60 deg C. using Hydrazine as the reducer resulting in a thickness of 0.5 microns. The pacing impedance of the plated electrode was then measured in a 0.18% NaCl solution using a nickel plate as the return electrode. The pacing pulse used was 5 volts and 0.5 ms. The impedance was found to be 250 ohms. This value was compared to a commercially available ablation electrode which was found to be 180 ohms. No damage to the coated electrode resulted.

EXAMPLE 5

A 1.6 mm diameter cable was sourced from MicroHelix in Portland Oreg. The cable contained 8 insulated wire coils in the wall of the tube. The insulating layer was a thin layer of PEBAX. Over one of the wires, a 4 mm length of insulation was removed to expose the corresponding amount of wire. A 4 mm band of the cable around the exposed wire was masked. Some plateable conductive ink from Creative Materials (CMI 117-31) Tyngsboro Mass. was coated around the unmasked region covering the exposed conductor.

The electrode ink was coated with a 3 micron layer of copper using electroless plating. The copper coated electrode was then immersed in an acid palladium chloride solution to catalyse the surface and immersed again in platinum complex electroless bath and coated for 1 hour at 60 deg C. using Hydrazine as the reducer. The pacing impedance of the plated electrode was then measured in a 0.18% NaCl solution using a nickel plate as the return electrode. The pacing pulse used was 5 volts and 0.5 ms. The impedance was found to be 120 ohms. This value was compared to a commercially available ablation electrode which was measure to be 180 ohms. No damage to the coated electrode resulted.

EXAMPLE 6

A 1.6 mm diameter cable was sourced from MicroHelix in Portland Oreg. The cable contained 8 insulated wire coils in the wall of the tube. The insulating layer was a thin layer of PEBAX. Over one of the wires, a 4 mm length of insulation was removed to expose the corresponding amount of wire. A 4 mm band of the cable around the exposed wire was masked. Some plateable conductive ink from Creative Materials (CMI 117-31) Tyngsboro Mass. was coated around the unmasked region covering the exposed conductor. The electrode ink was coated with a 3 micro layer of copper using electroless plating. The copper coated electrode was then immersed in an acid palladium chloride solution to catalyse the surface and immersed again in platinum complex electroless bath and coated for 1 hour at 60 deg C. using Hydrazine as the reducer.

The electrode was then placed on a piece of meat immersed in a 0.18% solution of NaCl and a stainless steel return electrode underneath. High frequency RF power was delivered through the electrode for 60 seconds, resulting in a lesion similar to a commercially available ablation electrode.

EXAMPLE 7

A 1.6 mm diameter cable was sourced from MicroHelix in Portland Oreg. The cable contained 8 insulated wire coils in the wall of the tube. The insulating layer was a thin layer of PEBAX. Over one of the wires, a 4 mm length of insulation was removed to expose the corresponding amount of wire. A 4 mm band of the cable around the exposed wire was masked. Some plateable conductive ink from Creative Materials (CMI 117-31) Tyngsboro Mass. was coated around the unmasked region covering the exposed conductor. The electrode ink was coated with a 3 micron layer of copper using electroless plating. The copper coated electrode was then immersed in an acid palladium chloride solution to catalyse the surface and immersed again in platinum complex electroless bath and coated for 1 hour at 60 deg C. using Hydrazine as the reducer.

The coated electrode was then immersed in a 0.18% NaCl solution using a nickel plate as the return electrode. A biphasic defibrillation pulse 130 volts in amplitude and 6 ms in pulse width was delivered through the coated electrode which resulted in no damage to the electrode and an impedance of 130 ohms.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are now described with reference to the accompanying drawings, in which:

FIGS. 1 a, 1 b and 1 c are side elevational views illustrating the construction of one embodiment of the present invention;

FIGS. 2 a, 2 b and 2 c are cross-sectional view through I-I of FIGS. 1 a, 1 b and 1 c respectively;

FIG. 3 is a side elevational view of a cut-away portion of an embodiment of the invention;

FIGS. 4 a and 4 b are part cut-away, part side elevational views of a further embodiment of the invention;

FIGS. 5 a and 5 b are side elevational views of a further embodiment of the invention;

FIG. 6 is a schematic view of a multi-electrode assembly incorporating electrically conductive regions of the present invention;

FIG. 7 is a perspective view of a number of electrically conductive regions of the present invention in an electrode assembly;

FIGS. 8 a, 8 b and 8 c are schematic views showing the steps of manufacture of an electrically conductive member according to a further aspect of the invention;

FIGS. 9 a, 9 b and 9 c are schematic views showing the steps of manufacture of an electrically conductive member of another embodiment of the aspect depicted in FIGS. 8 a, 8 b and 8 c; and

FIGS. 10 a, 10 b and 10 c are schematic views showing the steps of manufacture of an electrically conductive member of a further embodiment of the aspect depicted in FIGS. 8 a, 8 b and 8 c

DETAILED DESCRIPTION OF THE DRAWINGS

The lead 10 of the present invention includes an elongate body 11 having at least one electrically conductive region 20 thereof made from a porous polymeric material. The porous polymeric material is coated with an electrically conductive material and preferably a metal such as platinum.

As discussed above, the lead of the present invention is adapted for medical use and in particular use in cardiac mapping, defibrillation or pacing, neurological applications including neural stimulation implants, muscle stimulation, sensing and ablation.

As depicted in the drawings, the lead 10 has a tubular structure having a wall 12 and an internal lumen 13. While only one region 20 of the tube may be made from the porous polymeric material, it may be preferable that the entire length of the tube is made from said material.

The pores within the wall 12 are preferably greater than 5 microns and preferably between 30 and 100 microns.

The coating of the porous polymeric material with the metal creates a suitably thick layer of metal coating thereby increasing electrical conductivity through the lead 10.

To establish a good electrical connection the lead includes a conductive member 14.

In one embodiment, depicted in FIGS. 1 a, 1 b, 1 c, the conductive member 14 comprises a coiled wire 15 embedded within a wall 12 of the lead 10. The wire 15 is wrapped around and along a substantial length of the lead and preferably along the entire lead. While not shown, the wire 15 may pass through several pores of the polymeric material and thus when the porous polymer is coated with the metal, the portions of wire 15 within the pores may simultaneously be coated with the metal thereby creating a good electrical connection between wire and the at least one electrically conductive region 20.

As shown in FIGS. 1 a, 1 b and 1 c, the lead of this embodiment may be made in a number of stages. A first tube 16 is created as shown in FIG. 1 a. The tube 16 may, or may not be, porous in nature. The wire 15 is subsequently wrapped around and along the first tube 16 in a helical manner and the wire 15 and first tube 16 subsequently overlayed with a second porous polymer material 17.

In another embodiment, the conductive member 14 is a shape memory alloy spring 18 such as a Nitinol™ spring. The spring 18 of this embodiment is positioned internal the lumen 13 of the lead 10. In use, the spring 18 may be exposed to a pre-determined temperature that causes it to expand such that it abuts with the internal surface 19 of the lead 10. Preferably, the spring can normally expand to such an extent that its external diameter is greater than the diameter of the lumen 13 resulting in a good electrical connection between the spring and the at least one electrically conductive region.

In another embodiment of the invention depicted in FIGS. 5 a and 5 b, the conductive member 14 is adapted to engage one end 21 of the lead 10. Preferably the conductive member is a shape memory alloy tube 22 which is adapted to expand and increase its internal diameter upon heating above or cooling below a pre-determined temperature depending on the type of shape memory alloy. The shape memory alloy tube 22 may then be slid over the end 21 of the lead 10. Upon heating up or cooling below the pre-determined temperature depending on the type of shape memory alloy, the shape memory alloy tube 22 returns to its original unexpanded shape therefore effectively clamping down on an end of the lead as shown in FIG. 5 b. Accordingly, there is provided a uniform radial pressure on the end 21 of the lead 10 which results in a good electrical connection between the alloy tube and the at least one electrically conductive region. In this embodiment, it may be necessary to provide an inner, relatively stiff tube (not shown) which may be positioned internal the electrode 10 to prevent collapse of the lead 10.

Once the lead 10 has been coated with the selected metal, the lead 10 may be cut to the desired length depending on the application of the electrode. For example, a defibrillation electrode formed from the lead may need to be a length of around 60 mm whereas a lead acting as an electrode for mapping or sensing need only be a few millimetres in length.

A multi-electrode system along a lead may be constructed by threading together lengths of coated 23 or uncoated 24 tubes of specified lengths as depicted in FIG. 6. The coated 23 and uncoated 24 tubes are joined together using butt joints which may have spring or tubing supports (not shown) within the lumen of the tubes 23 or 24.

In the aspect of the invention depicted in FIGS. 8 a, 8 b and 8 c, the invention consists in an electrically conductive member 30 including an elongate body 31. The elongate body 31 has at least one electrically conductive region 32 which comprises a polymeric material together 33 together with at least one electrical conductor 34. A portion of the polymeric material 33 and a potion or all of the electrical conductor 34 are coated with an electrically conductive material 35.

The elongate body comprises a first cylindrical inner member 36 and a second outer member 37 said second outer member substantially forming a coating around the first inner member 36. The second outer member 37 extends substantially over the entire length of the first inner member 36. The at least one electrical conductor 34 is sandwiched between the first inner member 36 and the second outer member 37.

As shown in FIG. 8 b, the electrical conductor 34 is exposed. This may be achieved by a number of means including the application of heat, chemicals or lasers to remove the area of the outer member 37 covering the electrical conductor 34.

The exposed electrical conductor 34 and an area of the polymeric material 33 adjacent the electrical conductor 34 is then catalysed and coated with the electrically conductive material 35 to form an electrode 38.

As depicted in FIGS. 9 a, 9 b and 9 c, two electrodes 38 may be formed by coating separate electrical conductors 34 together with an adjacent area of polymeric material 33.

For high energy applications such as RF or microwave ablation, FIGS. 10 a, 10 b and 10 c show how a number of electrical conductors 34 together with their adjacent polymeric material 33 may be coated with an electrically conductive material to form a single electrode 38. The electrical conductors of this embodiment may be electrically connected to each other at a proximal end of each electrical conductor. The number of electrodes formed together with the spacing between each electrode may be varied.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. 

1-27. (canceled)
 28. A method of manufacturing an electrical lead, the method comprising: (i) extruding an elongate body of polymeric material wherein at least one region of the elongate body is porous in nature; and (ii) coating said elongate body with an electrically conductive material such that the electrically conductive material substantially coats the pores of said at least one region.
 29. The method of claim 28 wherein the electrically conductive material is applied to the elongate body by electroless plating.
 30. The method of claim 29 wherein the electrically conductive material is forced through the pores of the at least one electrically conductive region by the application of pressure.
 31. The method of claim 30 comprising a further step of one of electroplating and electroless plating.
 32. The method of claim 28 which includes, prior to step (ii), cleaning an outer surface of the elongate body.
 33. The method of claim 28 which includes, prior to step (ii), modifying an outer surface of the elongate body to produce a wettable or hydrophilic surface such that the deposition of the coating is accelerated and chemical and mechanical adhesion of the coating to the surface is improved.
 34. The method of claim 28 which includes, prior to step (ii), catalyzing a surface of the elongate body.
 35. The method of claim 34 which includes catalyzing a surface of only the at least one electrically conductive region of the elongate body. 36-56. (canceled) 